Connectors are widely used to attach and detach an electronic part, a cable, or the like to and from another part for mutual exchange of electrical power, a signal, or the like between the parts or between the part and the cable. A connector includes: a housing constituted by an insulator such as resin; and a contact constituted by metal. Such a contact needs to be pressed against a conductive member of a part to which it is connected, such as an electrode of a battery, so as to be in touch (sliding contact) with the conductive member. In order to maintain the touch, the contact is required to elastically deform in resistance to a load being applied to the contact along with the touch and, when the load has been removed, elastically deform to return to the state in which it had been before the application of the load.
FIG. 5 is a vertical cross-sectional view showing an example of a contact of a common battery connector. (a) of FIG. 5 shows a state in which no load is being applied, and (b) of FIG. 5 shows a state in which a load is being applied. In FIG. 5, a contact 200 includes: a retaining section 201, which is fixed by an insulator; a contact section 202, which makes sliding contact with a conductive member; and an elastic deformation section 203, which connects the retaining section and the contact section to each other and which is elastically deformable. The contact 200 is connected to a conductive member 204.
Sliding contact of the contact section 202 with the conductive member causes a load to be applied to the elastic deformation section 203, with the result that, as shown in (b) of FIG. 5, the elastic deformation section 203 elastically deforms. The larger the amount of displacement of the elastic deformation section 203 along with the application of the load is, i.e., the longer the stroke is, the larger the force of contact between the contact 200 and the conductive member 204 is. In this specification, the stroke for achieving necessary and sufficient contact force required of the contact is referred to as “long stroke”.
For a long stroke, it is necessary for the contact to be constituted by a material having a high spring bending elastic limit. Further, repetition of attachment and detachment with a long stroke causes the stress of a load to go beyond the acceptable range of stress, with the result that the contact is damaged by fatigue. Therefore, it is necessary to limit the stress of a load to the acceptable range of stress.
In order for the stress of a load to fall within the acceptable range of stress, it is necessary for the material constituting the contact to have a high tensile strength. Further, because the contact is used in applications where it is necessary to pass an electric current through the contact, a high conductivity is required. A low conductivity results in generation of heat due to power loss, thus making it impossible to pass an electric current. Further, from a point of view of energy conservation, a reduction in power loss is required.
Furthermore, in order for the contact to keep necessary contact force even after repetition of attachment and detachment, it is important for the elastic deformation section 203 not to exhibit a creep when the load has been removed. The term “creep” here means a time-dependent deformation of a material caused by constant stress at constant temperature.
That is, the occurrence of a creep causes the elastic deformation section 203 to remain strained when the load being applied to the elastic deformation section 203, for example, in the state of (b) of FIG. 5, has been removed, with the result that the elastic deformation section 203 does not return to its former state (state of (a) of FIG. 5). This renders the contact unable to keep the same contact force as before when it is brought into sliding contact with the conductive member again.
Patent Literature 1 discloses a contact formed into a spiral shape by using an electroformed layer made of a nickel-cobalt (NiCo) alloy having a fine average particle size of 20 nm or smaller. In the Patent Literature 1, the NiCo alloy has a fine particle size for higher strength. However, because, as confirmed in the comparative examples to be described later by the inventors of the present invention, a finer average particle size leads to notable occurrence of a creep, the contact is thought to be in a spiral shape for the purpose of suppressing the occurrence of a creep.